Imaging the Solar Winds as it Sweeps Past Earth

Data from STEREO's SECCHI Heliospheric Imagers have been used to image gusts in the solar wind as they go by the Earth

During relatively quiet solar conditions throughout the spring and summer of 2007, the SECCHI Heliospheric Imager HI-2 telescope on the STEREO-B spacecraft observed a succession of wave fronts sweeping past Earth. Scientists at the US Naval Research Laboratory have compared these images with local measurements of the solar wind obtained by near-Earth spacecraft. They found a perfect association between the occurrence of these waves and the arrival of high-density regions that rotate with the Sun.

These compression regions are believed to form when high-speed wind from dark areas of the solar corona known as coronal holes overtake and run into the low-speed wind in front of it. Currently, the researchers are tracking HI-2 waves backward toward the Sun to see exactly how they originate. Preliminary results suggest that the initial variations in the slow speed solar wind begin as blobs of material that are shed continuously from coronal streamers, large scale magnetic structures in the solar atmosphere.

In this movie Earth is the bright blob to the right. The long vertical streaks are the result of overexposure of bright objects, like planets, which are too bright for the sensitive detectors. The baffle on the right side of the image is a part of the HI2 that blocked out Earth when the STEREO spacecraft were even closer Earth and it appeared even brighter.